Electrically conductive coaxial guide wire

ABSTRACT

The present invention relates to A device for measurements, insertable into a living body, comprising an elongated flexible member ( 2, 30 ) with a proximal end and a distal end and a central lumen with an inner wall. The lumen is filled with a core ( 22 ) and an insulating material ( 21 ) is provided between the core and the inner wall; the core ( 22 ) is made of an electrically conductive material and has an essentially constant diameter over its entire length. An electrical sensor ( 44 ) is attached to the distal end of the elongated flexible member and is electrically connected ( 52 ) to the core ( 22 ).

BACKGROUND

1. Field of the Invention

The present invention relates generally to guide wire/sensor assemblies,wherein there are at least two electrical leads or conductors requiredfor energizing the sensor and for signal transmission, said leadsextending along the length of the guide wire between a proximal end anda distal end. In particular it relates to a coaxial, electricallyconductive guide wire provided with an electrical sensor.

2. Description of the Related Art

For medical purposes many devices and applications have been disclosedand patented, wherein a miniaturized sensor is positioned in the distalregion of a guide wire or a catheter. Such sensors can have variouspurposes, such as the measurement of pressure, temperature, flow, or forthe detection of some property in vivo in a living body, e.g., pH, O₂,CO₂, etc.

For most applications it is required that the sensors be energizedelectrically, and the response be transmitted back to the exterior ofthe patient via electrical signals. Some applications use optical sensordevices having fiber optic signal transmission, but these fall outsidethe scope of the present invention.

Thus, some means of signal and energy transmission is required, and mostcommonly extremely thin electrical leads are provided inside the guidewire, which itself is provided in the form of a tube (of the order of0.35 mm in outer diameter), oftentimes made of steel. In order toincrease the bending strength of the tubular guide wire, a core wire ispositioned inside the tube. The mentioned electrical leads arepositioned in the space between the inner lumen wall and the core wire.

This design has certain drawbacks. First, it renders the assemblynon-rotationally symmetric, since it is virtually impossible todistribute the electrical leads uniformly over the circumference of thecore wire inside the space between the inner lumen wall and the corewire. An asymmetric configuration of leads gives rise to differentbending properties in different directions of bending.

Second, there is a risk that the extremely thin leads (although coatedwith an insulating layer) will become damaged due to friction forcesappearing in the lumen, in particular at junctions in the proximal anddistal regions, where the core wire changes dimension, and wheremanipulations during manufacture (e.g. soldering) can cause damage tothe coating and possibly cause a short-circuit.

Third, it is relatively complicated to assemble the device because ofthe extremely small dimensions of tubes, leads and sensors. And, fourth,electrical contacts at the proximal end of the guide wire are made usingdiscrete components, thereby complicating the assembly.

A guide wire disclosed in EP 0 925 803, assigned to the same assignee asthe present invention, attempts to solve the symmetry problem byproviding electrical leads in the form of concentric layers ofconducting material with insulation provide between layers. Althoughrepresenting an improvement, this device also has certain drawbacks. Forexample, there is a risk that the concentric layers may break and causea short-circuit. Another possible problem could be “pinholes” in thevery thin insulating layers, representing a potential risk forshort-circuiting.

SUMMARY

Thus, in view of the problems with the prior art devices, it is theobject of the present invention to provide a guide wire design thatovercomes the drawbacks of the prior art sensor/guide wire assemblydesigns.

Therefore, a measuring device, insertable into a living body, isprovided which comprises an elongated flexible member having a proximalend and a distal end and a central lumen with an inner wall, a corefilling said lumen, an insulating material provided between said coreand said inner wall, said core being made of an electrically conductivematerial and having an essentially constant diameter over its entirelength, an electrical sensor attached to the distal end of saidelongated flexible member, said electrical sensor being electricallycoupled to said core.

By making the guide wire from a coaxial wire, in particular having acentral core of essentially constant diameter, the cost of manufacturingis lowered and the complexity by which the guide wire is manufactured isreduced.

The manufacturing process can be implemented as a continuous process,wherein long lengths of wire can be made, as opposed to the prior artdevice, where the wire must be made piece by piece.

Also, the guide wire becomes rotationally symmetric, which is asignificant advantage in terms of ease of manipulation of the device bya physician when using the device.

Furthermore, the structure is much less prone to develop “pin holes”that could lead to short circuiting problems.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe attached drawings, in which

FIG. 1 is a longitudinal cross-sectional view through a prior art guidewire according to EP 0 925 803;

FIG. 2 is a cross-sectional view through a first embodiment of a coaxialguide wire suitable for use in the invention;

FIG. 3 is a schematic cross-section in the longitudinal direction of aguide wire suitable for use according to the invention;

FIG. 4A shows, in greater detail, the distal end portion with a sensormount, and a sensor mounted therein, in a top view;

FIG. 4B shows a cross sectional view in longitudinal direction of thedevice shown in FIG. 4A;

FIG. 5A shows a cross sectional view taken along line 5A—5A in FIG. 4B;

FIG. 5B shows a cross sectional view taken along line 5B—5B in FIG. 4B;

FIG. 5C shows a cross sectional view taken along line 5C—5C in FIG. 4B;

FIG. 6A shows a cross sectional view of a second embodiment of a coaxialguide wire suitable for use in the invention;

FIG. 6B is a longitudinal cross sectional view through a sensor andguide wire assembly according to a second embodiment, namely the distalend portion with a sensor mount, and a sensor mounted therein;

FIG. 7A shows a proximal contact;

FIG. 7B shows a second embodiment of a proximal contact; and

FIG. 8 illustrates a further embodiment of a sensor and guide wireassembly according to the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a prior art guide wire according to EP 0 925 803 incross section in the longitudinal direction. It comprises a core wire 2,on which a plurality of concentric layers 4, 6 of conductive materialhave been provided. Between the conductive layers there are insulatinglayers 10, 12, and another insulating layer 14 is provided on top oflayer 6. In addition to the drawbacks mentioned in the discussion of thebackground of the invention, the manufacturing process is rathercomplex, either by a complex extrusion process or by a process involvinga consecutive deposition of the various layers.

FIG. 2 illustrates the key feature of the present invention. It shows across section through a guide wire 20 having a central core 22 of aconductive material (e.g. stainless steel or superelastic metal (e.g.Nitinol®)) disposed within the lumen of a thick-walled tube 24 also of aconductive material (e.g. stainless steel or superelastic metal (e.g.Nitinol®)). There is an insulating layer 21 between the core 22 and thetube 24.

This structure of the core/insulator/tube can suitably be manufacturedby an extrusion process, or by shrinking a tube onto a core. Thus, thecore is located inside the tube in a tight fit. The outer surface of thetube 24 is preferably covered by an insulating layer 23, in order toprotect the wire from blood and other fluids, which could otherwisecause short circuiting. The insulating material usable with theinvention for the outer surface layer 23, can e.g. be selected among anumber of polymer materials, Teflon®, poly-imide or Parylene™, just tomention a few. Also ceramic type materials, e.g. alumina or siliconnitride, in its various possible forms can be used. For the intermediatelayer 21, however, the ceramic materials are not suitable, and thereforpolymer materials of the same type as mentioned above are usable.

The diameter of the core over its entire length is constant, and issuitably less than 50% of the outer diameter of the elongated flexiblemember (and is preferably less than 25% thereof), except in the distalend, where the outer layer is reduced in order to provide the necessaryconstructive details, as later described.

The constant diameter of the core is a significant advantage over theprior art structure according to EP 0 925 803, in that it makes possiblea continuous manufacturing process whereas the '803 structure must bemade piece by piece. Thus, by using a coaxial wire according to theteachings herein, the manufacturing time will be considerably reducedand simplified, and therefore, much more economical.

Other great benefits of this structure include: (a) that it isrotationally symmetric; (b) that the torque can be controlled bycontrolling the relative dimensions of core and tube; and (c) that themounting of a sensor element on the guide wire becomes very simple, aswill later be described in further detail.

FIG. 3 is a schematic view of an embodiment of an elongated flexiblemember forming a guide wire, generally designated with reference numeral30, having the basic construction of FIG. 2, however shown withoutcertain details at the distal end (protective coil, sensor etc). Thevarious segments of the wire are not shown to scale, and the totallength of the wire is typically about 1.80 meters, although otherlengths are possible, even up to about 3 meters.

As can be seen in FIG. 3 the diameter of the elongated flexible membervaries, and in the distal end has segments of reduced diameter toincrease the flexibility of the wire in the distal region. However, thevery distal end portion 32, which comprises a thicker portion forming amounting structure for the sensor, has a thickness corresponding to thediameter of the wire in its proximal region (e.g. approximately 0.35mm).

This thicker portion 32 comprises a mount (shown in FIGS. 4 a and 4 b)for a sensor element. This mounting structure comprises a recess, havinga bottom surface in a first portion of which the core is exposed so asto form a first contact surface for the sensor (i.e., the mountingstructure forms an arrangement which is in accordance with the teachingsof our U.S. Pat. No. 6,142,958 (incorporated herein by reference)).

FIGS. 4A and 4B illustrate the distal end portion 32 of one embodimentin greater detail. FIG. 4A shows the sensor mount in a top view and FIG.4B shows a side view with parts in cross section. FIGS. 5A–5C are crosssections taken along lines 5A—5A, 5B—5B, and 5C—5C, respectively.

Thus, the thicker distal sensor mount portion 32 has a recess 40 formedtherein (which is formed by suitable machining, e.g., EDM cutting orlaser cutting) which constitutes said sensor mount for a miniaturizedsensor 44. Thereby, the bottom surface of the recess will exhibit tworegions of conductive material. Namely, the central core 22 (indicatedwith broken lines in the part not shown in cross section) will beexposed to form a first contact surface 46, separated from the bulkmaterial of the tube by the insulation material 21. The bulk material ofthe tube will form a second contact surface 48.

A sensor chip 44 having two contact terminals 50, 52 (located on thebottom side of the sensor chip, indicated by circles in broken lines),can thus be attached by suitable bonding or soldering to these surfaces,as can be seen in FIG. 4B. In this way, electrical energy can besupplied for energizing purposes in the two leads formed by the core andthe tube, respectively. By suitable techniques for modulation of theenergizing current, the same leads can be used for signal transmission.

In the shown embodiment, the recess 40 has a deeper portion 54 in theregion where the sensitive part of the sensor chip 44 is positioned,such that the sensitive part of the chip extends out over the deeperrecess part 54, which is seen in FIG. 4B. This is in accordance with theteachings in our U.S. Pat. No. 6,112,598 (incorporated herein byreference), and reduces or even eliminates bending artifacts.

The recess in this embodiment reaches through the core 22.

In an alternative design, the deeper recess portion can extend all theway through the thicker portion, as indicated by broken lines 56 in FIG.4B. Such a design would yield a cross section of the type shown in FIG.5C which is taken along line 5C—5C in FIG. 4B.

In this embodiment the diameter of the enlarged sensor mount portion 32has the same diameter as the diameter of the guide wire. Therefore, itis not possible to attach the coil 59 by sliding it over the wire.Instead it must be wound onto the wire at the correct position, i.e.,proximally of the sensor mount.

FIG. 5A shows a cross section taken along line 5A—5A in FIG. 4B. Here itcan be clearly seen how the sensor chip 44 is attached to the twocontact surfaces 46 and 48, respectively, by the contact terminals 50,52 respectively.

An alternative way of connecting the sensor chip to the outer tube is bybonding an electrical lead 53 thereto. Thereby eliminating the contactterminal 52.

FIG. 5B shows the cross section taken along line 5B—5B in FIG. 4B, whichclearly illustrates the “cantilevering” end of the sensor chip.

In order not to short circuit the core 22 and the outer tube material32, when the recess is exposed to body fluids, the inner surface of therecess must be covered with some protective material 58 (not shown inFIGS. 5A–5C). This can be easily achieved by providing silicone or somesimilar material to cover at least those areas where fluids could causea short circuit.

In the embodiment described above with reference to FIGS. 4–5, the corehas a relatively small diameter compared to the surrounding tube.However, it is also possible to make a coaxial guide wire 60 with athicker core 62, and a thinner outer tube 66 with an insulating layer 64provided between the core and the tube, as shown in FIG. 6A. Inaddition, preferably an insulating layer 63 is applied to the outersurface of the tube 66.

In this embodiment, the recess 68 forming the sensor mount will notreach all the way through the core 62, as can be seen in FIG. 6B. Thisrequires that the entire bottom surface and parts of the walls of therecess 68 be covered with insulating material 67. It also necessitatesprotection of the distal end surface 69 of the core with insulatingmaterial 67 b so that the very distal tip 65 that is to be attachedthereto will not be in electrical contact with the inner core 62. Forthe purpose of securing the tip 65, it is convenient to provide a pieceof tubing 61 over the enlarged portion forming the sensor mount.

This piece of tubing extends slightly beyond the distal end 69, so as toform a cylindrical recess in which the proximal end of the tip 65 can beinserted, and secured by soldering, gluing, or shrinking. Thus, in thiscase the sensor mount has a diameter that is smaller than the diameterof the wire 60. Therefore, in this case the coil 59 can be slid over themount and secured by soldering or gluing, before the piece of tubing 61is positioned on the mount.

In a further advantageous aspect of the invention, the novel guide wiredesign provides for a very simple way to construct a proximal maleconnector, for connecting the guide wire assembly to external equipment.

In FIG. 7A the proximal end 70 of a guide wire 80 is shown in crosssection. It comprises an outer tube member 72, an inner core 74 with aninsulating layer 75 disposed between said core and said tube.

In order to make a connector having two contact elements or surfaces, acircumferential recess 71 is made in the outer tube 72, down to theinsulating layer 75 (this embodiment is shown in FIG. 7A), or throughthe insulating layer 75 down to a depth at which the inner core 74 isexposed (FIG. 7B). It is of course essential that there be no electricalconnection between the distal and the proximal end of the outer tube.The recess is filled with an insulating material 76, e.g. some polymer(Teflon®, poly-imide or Parylene or the like) or an inorganic materialsuch as ceramic type materials, e.g. alumina or silicon nitride, in itsvarious possible forms.

Finally, the very end surface of the coaxial wire 80 is “capped” with alayer 78 of conductive material so as to short circuit the core 74 withthe proximal end portion of the tube, now electrically insulated fromthe remainder of the tube on the distal side of the recess 71 filledwith insulating material 76.

FIG. 8 illustrates an alternative way of providing the sensor mount atthe distal end of the wire.

It encompasses providing a tube segment 82 having an inner diametercorresponding to the outer diameter of the coaxial wire 84, andpositioning said tube segment 82 over the distal end of the wire 84.Thereby a portion of the tube segment 82 should extend around the wire84 so as to form a cylindrical recess 86 at the distal end. This recesswill be used for attaching a tip 88 by press fitting and/or soldering.

When the tube 82 is mounted on the wire 84, a recess 90 is formed by anysuitable technique, e.g., EDM cutting or laser cutting, down to a depthsuch that the inner core 92 is exposed. The exposed bottom surface 94can be used as a first contact surface for a sensor element (not shown).The walls 96 of the recess 90 can be used as a second contact surfacefor said sensor.

1. A measuring device adapted to be inserted into a living body, thedevice comprising: an elongated flexible member having a proximal endand a distal end and a central lumen formed in a thick-walled tube withan inner wall; a core provided in said lumen, said core being made of anelectrically conductive material and having an essentially constantdiameter over its entire length; an insulating material provided betweensaid core and said inner wall; and an electrical sensor attached to thedistal end of said elongated flexible member, said electrical sensorbeing electrically coupled to said core; wherein said core is providedinside said lumen, substantially along the entire length of theelongated flexible member, in a tight fit, and wherein a diameter of thecore, substantially along the entire length of the elongated flexiblemember, is less than about 50% of an outer diameter of the elongatedflexible member.
 2. The device as claimed in claim 1, wherein saidelongated flexible member is rotationally symmetric.
 3. A measuringdevice adapted to be inserted into a living body, the device comprising:an elongated flexible member having a proximal end and a distal end anda central lumen with an inner wall; a core provided in said lumen, saidcore being made of an electrically conductive material and having anessentially constant diameter over its entire length; an insulatingmaterial provided between said core and said inner wall; and anelectrical sensor attached to the distal end of said elongated flexiblemember, said electrical sensor being electrically coupled to said core;wherein the diameter of the core, except in the distal region, is lessthan about 25% of the outer diameter of the elongated flexible member;and wherein a diameter of the elongated flexible member comprisessegments in the distal region having varying diameters.
 4. The device asclaimed in claim 3, wherein the lumen is formed in a thick-walled tube.5. A measuring device adapted to be inserted into a living body, thedevice comprising: an elongated flexible member having a proximal endand a distal end and a central lumen with an inner wall; a core providedin said lumen, said core being made of an electrically conductivematerial and having an essentially constant diameter over its entirelength; an insulating material provided between said core and said innerwall; and an electrical sensor attached to the distal end of saidelongated flexible member, said electrical sensor being electricallycoupled to said core; wherein said core is provided inside said lumen,substantially along the entire length of the elongated flexible member,in a tight fit, and wherein a diameter of the core, substantially alongthe entire length of the elongated flexible member, is less than about50% of an outer diameter of the elongated flexible member; and whereinsaid elongated flexible member, at its distal end, comprises a thickerportion forming a mounting structure for said sensor, and wherein saidmounting structure comprises a recess having a bottom surface in a firstportion of which the core is exposed so as to form a first contactsurface for said sensor.
 6. A measuring device adapted to be insertedinto a living body, the device comprising: an elongated flexible memberhaving a proximal end and a distal end and a central lumen with an innerwall; a core provided in said lumen, said core being made of anelectrically conductive material and having an essentially constantdiameter over its entire length; an insulating material provided betweensaid core and said inner wall; and an electrical sensor attached to thedistal end of said elongated flexible member, said electrical sensorbeing electrically coupled to said core; wherein said elongated flexiblemember, at its distal end, comprises a thicker portion forming amounting structure for said sensor, and wherein said mounting structurecomprises a recess having a bottom surface in a first portion of whichthe core is exposed so as to form a first contact surface for saidsensor; and wherein said elongated flexible member is made of aconductive material, and wherein the conductive material of saidelongated flexible member in a second portion of said bottom surfaceforms a second contact surface for said sensor.
 7. A measuring deviceadapted to be inserted into a living body, the device comprising: anelongated flexible member having a proximal end and a distal end and acentral lumen with an inner wall; a core provided in said lumen, saidcore being made of an electrically conductive material and having anessentially constant diameter over its entire length; an insulatingmaterial provided between said core and said inner wall; and anelectrical sensor attached to the distal end of said elongated flexiblemember, said electrical sensor being electrically coupled to said core;wherein said core is provided inside said lumen, substantially along theentire length of the elongated flexible member, in a tight fit, andwherein a diameter of the core, substantially along the entire length ofthe elongated flexible member, is less than about 50% of an outerdiameter of the elongated flexible member; and wherein said elongatedflexible member, at its distal end, comprises a mounting structure forsaid sensor, wherein said mounting structure comprises a recess, whereinthe recess has a bottom surface in a first portion of which the core isexposed so as to form a first contact surface for said sensor, andwherein said mounting structure has a diameter that is smaller than adiameter of the flexible member.
 8. A measuring device adapted to beinserted into a living body, the device comprising: an elongatedflexible member having a proximal end and a distal end and a centrallumen with an inner wall; a core provided in said lumen, said core beingmade of an electrically conductive material and having an essentiallyconstant diameter over its entire length; an insulating materialprovided between said core and said inner wall; and an electrical sensorattached to the distal end of said elongated flexible member, saidelectrical sensor being electrically coupled to said core; wherein saidelongated flexible member, at its distal end, comprises a mountingstructure for said sensor, wherein said mounting structure comprises arecess, wherein the recess has a bottom surface in a first portion ofwhich the core is exposed so as to form a first contact surface for saidsensor, and wherein said mounting structure has a diameter that issmaller than a diameter of the flexible member; wherein said elongatedflexible member is made of a conductive material; and wherein theconductive material of said elongated flexible member in a secondportion of said bottom surface forms a second contact surface for saidsensor.
 9. A measuring device adapted to be inserted into a living body,the device comprising: an elongated flexible member having a proximalend and a distal end and a central lumen with an inner wall; a coreprovided in said lumen, said core being made of an electricallyconductive material and having an essentially constant diameter over itsentire length; an insulating material provided between said core andsaid inner wall; and an electrical sensor attached to the distal end ofsaid elongated flexible member, said electrical sensor beingelectrically coupled to said core; wherein said elongated flexiblemember, at its distal end, comprises a mounting structure for saidsensor, wherein said mounting structure comprises a recess, wherein therecess has a bottom surface in a first portion of which the core isexposed so as to form a first contact surface for said sensor, andwherein said mounting structure has a diameter that is smaller than adiameter of the flexible member; wherein said elongated flexible memberis made of a conductive material; and wherein a protective material isprovided in said recess which is adapted to prevent a short circuitbetween the core and the conductive material of the elongated flexiblemember.
 10. A measuring device adapted to be inserted into a livingbody, the device comprising: an elongated flexible member having aproximal end and a distal end and a central lumen with an inner wall; acore provided in said lumen, said core being made of an electricallyconductive material and having an essentially constant diameter over itsentire length; an insulating material provided between said core andsaid inner wall; and an electrical sensor attached to the distal end ofsaid elongated flexible member, said electrical sensor beingelectrically coupled to said core; and a connector at the proximal end,comprising: a circumferential recess in the elongated flexible memberextending at least down to the insulating material, the recess beingfilled with an insulation so as to ensure that there is no electricalconnection between the proximal part and the distal part of theelongated flexible member, and a proximal end cap, short circuiting thecore and the proximal part of the elongated flexible member.
 11. A guidewire and sensor assembly comprising: an elongated flexible membercomprising: a thick-walled tube having an inner lumen; a core providedin said lumen in a tight fit, wherein said core has an essentiallyconstant diameter over the entire length of said elongated flexiblemember, the constant diameter being less than about 50% of an outerdiameter of the tube, and wherein said tube and said core are made of anelectrically conductive material; and an insulating layer providedbetween said core and said tube; and a sensor located at the distal endof the assembly and in electrical contact with the core and the tube.12. A guide wire and sensor assembly comprising: an elongated flexiblemember comprising: a thick-walled tube having an inner lumen; and a coreprovided in said lumen in a tight fit, wherein said core has anessentially constant diameter and is provided in the tight fit over theentire length of said elongated flexible member, wherein said core ismade of an electrically conductive material, and wherein said tube ismade of an insulating non-conductive material; and a sensor located atthe distal end of the assembly and in electrical contact with the core.13. A guide wire and sensor assembly comprising: an elongated flexiblemember comprising: a tube having an inner lumen; a core provided in saidlumen in a tight fit, wherein said core has an essentially constantdiameter over the entire length of said elongated flexible member, andwherein said tube and said core are made of an electrically conductivematerial; and an insulating layer provided between said core and saidtube; and a sensor located at the distal end of the assembly and inelectrical contact with at least the core; wherein a diameter of theelongated flexible member comprises segments in the distal region havingvarying diameters, and wherein the diameter of the core, except in thedistal region, is less than about 25% of the outer diameter of theelongated flexible member.
 14. The guide wire and sensor assembly asclaimed in claim 13, wherein the tube is a thin-walled tube.
 15. A guidewire and sensor assembly comprising: an elongated flexible membercomprising: a tube having an inner lumen; a core provided in said lumenin a tight fit, wherein said core has an essentially constant diameterover the entire length of said elongated flexible member, and whereinsaid tube and said core are made of an electrically conductive material;and an insulating layer provided between said core and said tube; and asensor, located at the distal end of the assembly and in electricalcontact with at least the core; wherein a diameter of the elongatedflexible member comprises segments in the distal region having varyingdiameters; and wherein the diameter of the core, except in the distalregion, is less than about 25% of the outer diameter of the elongatedflexible member.
 16. The guide wire and sensor assembly as claimed inclaim 15, wherein the tube is a thin-walled tube.
 17. A guide wire andsensor assembly comprising: an elongated flexible member comprising: atube having an inner lumen; a core provided in said lumen in a tightfit, wherein said core has an essentially constant diameter over theentire length of said elongated flexible member; and wherein said tubeand said core are made of an electrically conductive material; aninsulating layer provided between said core and said tube; and a sensorlocated at the distal end of the assembly and in electrical contact withat least the core; wherein a diameter of the elongated flexible membercomprises segments in the distal region having varying diameters,wherein the diameter of the core, except in the distal region, is lessthan about 50% of the outer diameter of the elongated flexible member,wherein said elongated flexible member is rotationally symmetric,wherein said elongated flexible member is made of a conductive material,wherein said elongated flexible member at its distal end comprises amounting structure for said sensor, wherein said mounting structurecomprises a recess, wherein the recess has a bottom surface in a firstportion of which the core is exposed so as to form a first contactsurface for said sensor, and wherein the conductive material of saidelongated flexible member in a second portion of said bottom surfaceforms a second contact surface for said sensor.
 18. The guide wire andsensor assembly as claimed in claim 17, wherein the diameter of thecore, except in the distal region, is less than about 25% of the outerdiameter of the elongated flexible member.
 19. A measuring deviceadapted to be inserted into a living body, the device comprising: anelongated flexible member having a proximal end and a distal end and acentral lumen formed in a thick-walled tube with an inner wall; a coreprovided in said lumen, said core being made of an electricallyconductive material and having an essentially constant diameter over itsentire length; an insulating material provided between said core andsaid inner wall; and an electrical sensor attached to the distal end ofsaid elongated flexible member, said electrical sensor beingelectrically coupled to said core; wherein the diameter of the core,except in the distal region, is less than about 25% of the outerdiameter of the elongated flexible member.
 20. The device as claimed inclaim 19, wherein said core is provided inside said lumen in a tightfit.
 21. A measuring device adapted to be inserted into a living body,the device comprising: an elongated flexible member having a proximalend and a distal end and a central lumen formed in a thick-walled tubewith an inner wall; a core provided in said lumen, said core being madeof an electrically conductive material and having an essentiallyconstant diameter over its entire length; an insulating materialprovided between said core and said inner wall; and an electrical sensorattached to the distal end of said elongated flexible member, saidelectrical sensor being electrically coupled to said core; wherein saidcore is provided inside said tube in a tight fit; and wherein a diameterof the core, except in the distal region, is less than about 25% of anouter diameter of the elongated flexible member.
 22. A measuring deviceadapted to be inserted into a living body, the device comprising: anelongated flexible member having a proximal end and a distal end and acentral lumen formed in a thick-walled tube with an inner wall; a coreprovided in said lumen, said core being made of an electricallyconductive material and having an essentially constant diameter over itsentire length; an insulating material provided between said core andsaid inner wall; and an electrical sensor attached to the distal end ofsaid elongated flexible member, said electrical sensor beingelectrically coupled to said core; wherein the measuring device,substantially along the entire length of the elongated flexible member,is rotationally symmetric.
 23. A guide wire and sensor assemblycomprising: an elongated flexible member comprising: a tube having aninner lumen; a core provided in said lumen, wherein said core has anessentially constant diameter over a substantial portion of the lengthof the tube, wherein the constant diameter of the core, substantiallyalong the entire length of the tube, is about the same as a wallthickness of the tube substantially along the entire length of the tube,and wherein said tube and said core are made of an electricallyconductive material; an insulating layer provided between said core andsaid tube; and a sensor located at the distal end of the assembly and inelectrical contact with the core and the tube.